// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// The GZipHeader class allows you to parse a gzip header, such as you
// might find at the beginning of a file compressed by gzip (ie, a .gz
// file), or at the beginning of an HTTP response that uses a gzip
// Content-Encoding. See RFC 1952 for the specification for the gzip
// header.
//
// The model is that you call ReadMore() for each chunk of bytes
// you've read from a file or socket.
//

#ifndef NET_FILTER_GZIP_HEADER_H_
#define NET_FILTER_GZIP_HEADER_H_

#include <stdint.h>

#include "base/macros.h"

namespace net {

class GZipHeader {
public:
    enum Status {
        INCOMPLETE_HEADER, // don't have all the bits yet...
        COMPLETE_HEADER, // complete, valid header
        INVALID_HEADER, // found something invalid in the header
    };

    GZipHeader();
    ~GZipHeader();

    // Wipe the slate clean and start from scratch.
    void Reset();

    // Attempt to parse the given buffer as the next installment of
    // bytes from a gzip header. If the bytes we've seen so far do not
    // yet constitute a complete gzip header, return
    // INCOMPLETE_HEADER. If these bytes do not constitute a *valid*
    // gzip header, return INVALID_HEADER. When we've seen a complete
    // gzip header, return COMPLETE_HEADER and set the pointer pointed
    // to by header_end to the first byte beyond the gzip header.
    Status ReadMore(const char* inbuf,
        int inbuf_len,
        const char** header_end);

private:
    enum { // flags (see RFC)
        FLAG_FTEXT = 0x01, // bit 0 set: file probably ascii text
        FLAG_FHCRC = 0x02, // bit 1 set: header CRC present
        FLAG_FEXTRA = 0x04, // bit 2 set: extra field present
        FLAG_FNAME = 0x08, // bit 3 set: original file name present
        FLAG_FCOMMENT = 0x10, // bit 4 set: file comment present
        FLAG_RESERVED = 0xE0, // bits 5..7: reserved
    };

    enum State {
        // The first 10 bytes are the fixed-size header:
        IN_HEADER_ID1,
        IN_HEADER_ID2,
        IN_HEADER_CM,
        IN_HEADER_FLG,
        IN_HEADER_MTIME_BYTE_0,
        IN_HEADER_MTIME_BYTE_1,
        IN_HEADER_MTIME_BYTE_2,
        IN_HEADER_MTIME_BYTE_3,
        IN_HEADER_XFL,
        IN_HEADER_OS,

        IN_XLEN_BYTE_0,
        IN_XLEN_BYTE_1,
        IN_FEXTRA,

        IN_FNAME,

        IN_FCOMMENT,

        IN_FHCRC_BYTE_0,
        IN_FHCRC_BYTE_1,

        IN_DONE,
    };

    static const uint8_t magic[]; // gzip magic header

    int state_; // our current State in the parsing FSM: an int so we can ++
    uint8_t flags_; // the flags byte of the header ("FLG" in the RFC)
    uint16_t extra_length_; // how much of the "extra field" we have yet to read

    DISALLOW_COPY_AND_ASSIGN(GZipHeader);
};

} // namespace net

#endif // NET_FILTER_GZIP_HEADER_H_
